Studies on the hepatic excretion of organic anions are being performed both in vivo and in vitro. In either anesthetized, acutely nephrectomized rats the rate of the biliary excretion of iopanoate glucuronide is one-fifth that obtained in urethane anesthetized animals. The indications are that this difference is not attributable to a simple mechanism since the rate of excretion of another organic anion, bromosulfophthalein, is essentially the same in both ether anesthetized and urethane anesthetized animals. The possibility exists that there is a step in the overall transport mechanism for iopanoate that is not shared by bromosulfophthalein, and that this step is uniquely sensitive to the actions of certain anesthetics. It should be possible to determine the characteristics of this step by analyzing the effect of the anesthetics on liver perfusion, intracellular binding and metabolism. These data would be important to overall understanding of the hepatic transport of organic anions since most experimental procedures aimed at elucidating hepatic transport mechanisms require the use of anesthetized preparations. It is therefore conceivable that studies that are designed to study the competition for excretion of organic anions may, in fact, be subject to an undetermined drug interaction, the anesthetic. These studies will be pursued to determine the range of compounds that are thus effected and to determine the nature of the anesthetic effect by utilizing both in vivo and in vitro model systems.